The Only Solution for Roads full of Potholes: Mandatory use of Dense Bituminous Mixes
The Only Solution for Roads full of Potholes: Mandatory use of Dense Bituminous Mixes
Why we have potholes on bituminous roads especially during monsoons?
Recently, I happened to meet a young, conscientious and inquisitive highway engineer on a road project. The following Q and A ensued (questions from him and answers from me), which I am sure would be of interest to you. Even if you are not an engineer you will understand it.
Why bituminous roads in India develop potholes prematurely especially during monsoons? This gives the impression that concrete roads are better.
Whereas quality of materials and construction are important, there is a fundamental highway engineering requirement that the bituminous mix used in road construction should be dense so that water cannot penetrate it. Even the “aam aadmi” knows (many of our highway engineers ignore it) that water is Enemy Number 1 of bitumen and can destroy the road regardless whether it is a rural road or a national highway. This means we should not use the so-called “semi dense” or “open” graded bituminous mixes in any road construction, which give an open invitation to water. However, such mixes are permitted and used across India on a wide scale.
Why do we permit such bituminous mixes which are obviously prone to water intrusion?
Road specifications issued by the Ministry of Road Transport and Highways (MORTH) contain 10 types of bituminous mixes which can be categorized as dense, semi dense, and open graded. This book of specifications is popularly called “orange book” because it has orange colour cover. Unfortunately, this orange book is considered by many Indian highway engineers as “Gita” of specifications. That means any bituminous mix listed in this book (good or bad) is sacred and you can use it with confidence. There is no way you can remove any mix because they all are “good”.
Can you list which mixes are dense, semi dense and open graded?
Yes, I can.
Dense graded bituminous mixes
DBM Grading 2
BC Grading 1
BC Grading 2
[Note: DBM Grading 1 is not listed because due to large nominal aggregate size of 37.5 mm it is permeable to water and fails prematurely.]
Semi dense graded bituminous mixes
SDBC Grading 1
SDBC Grading 2
Mixed Seal Surfacing (MSS)
Open graded bituminous mixes
BM Grading 1
BM Grading 2
Premix carpet (PMC) with seal coat
This means of the 10 bituminous mixes listed in the MORTH orange book, seven are not desirable. These seven mixes are either semi dense or open graded and therefore would easily “invite” water during monsoons and fail prematurely. Is that correct?
Yes, that is correct.
Are there any published technical papers in India to support the contention that these seven semi dense or open mixes are not desirable and therefore should not be used?
Yes. Three technical papers (authored by me and co-authored by Prof. Veeraragavan of IIT Madras) have been published by the Indian Roads Congress (IRC) since 2008 and also presented as formal papers in IRC annual sessions. The third one was presented this year (November 2017) at IRC’s Bangalore Session. [I am attaching a copy of that paper.] Recent research work at IIT Guwahati has shown similar results.
Why engineers in MORTH and the Indian Roads Congress (IRC) do not pay any attention to published technical papers and delete these undesirable bituminous mixes from their specifications?
That is a good question! MORTH, NHAI and IRC appear to be dominated by the serving and retired MORTH and PWD engineers who generally believe in status quo. Many open bituminous mixes such as BM and PMC were developed long time ago when we did not hot mix plants which are capable of producing dense bituminous mixes. Now, we have numerous hot mix plants all over India. But our “status quo” engineers just want to hang on to outdated technologies just like the telephone models.
Why not these “status quo” engineers prepare a technical paper to justify the use of the seven semi dense and open bituminous mixes in the specifications?
I do not think they can. The fundamentals of highway engineering are not on their side.
Then how do they respond when asked?
They just give vague answers such as follows:
· These mixes are good for India; they have served us well.
· I have tried these mixes, they really work.
· India cannot afford dense mixes. [Although the relatively cheap bituminous mixes may last for 1-2 year, which is bad economics.]
Unfortunately, these engineers are very good at convincing their bosses: both bureaucrats and politicians to maintain the status quo.
Why our IITs and NITs do not conduct research on these 10 bituminous mixes? That appears to be the need of the hour.
That is a good question. I believe many of them are more interested in trying exotic or strange materials in bituminous mixes. Even the Central Road Research Institute (CRRI) should take cognizance of this subject after reading our three IRC technical papers and give their frank, technical opinion to MORTH and IRC in nation’s interest. Unfortunately, they have not. Nobody wants to create any waves.
What about Indian highway engineers at large both in public and private sector? Do they support this cause?
I believe a “silent majority” does. But most of them (including the academia) appear to be afraid to come out in the open and support this technically justified cause which is truly in India’s interest. I do not understand why they are so afraid in writing to MORTH and IRC.
Are semi dense or open graded mixes used in developed countries?
No. Those countries concur with Indian “aam aadmi” opinion that water is Enemy Number 1 of bitumen and eventually destroys it.
“Aam aadmi” in India believes our highway engineers intentionally construct “bad” roads so they can get “fat” road budget year after year. Your comment?
I have no comment.
Based on your experience as a practicing highway engineer (over 30 years in the US and over 20 years in India), which bituminous mixes you recommend for India?
I recommend the following three dense graded bituminous mixes only for all types of roads; these mixes are already in the orange book (no options or exceptions should be permitted):
Base Course DBM Grading 2 (nominal aggregate size 25 mm)
Binder Course BC Grading 1 (nominal aggregate size 19 mm)
Wearing Course BC Grading 2 (nominal aggregate size 12.5 mm)
Open graded premix carpet (PMC) is used extensively on our rural roads such as Pradhan Mantri Grameen Sadak Yojna (PMGSY). It should be replaced with mechanized surface dressing with precoated aggregate, which effectively waterproofs the road, thus minimizing potholes. Surface dressing costs only 40 percent of what PMC does and would last much longer. This step would revolutionize the PMGSY program by saving thousands of crores of rupees every year and increasing the life of rural roads. It should be noted that NO country in the world would like to use “water-trapping” open graded PMC; they prefer surface dressing on low to medium traffic roads. Is Hon. Prime Minister Modi listening?
Bad roads are a genuine national problem. So many people are dying from potholes everyday what to talk about the inconvenience and crores of rupees being wasted by using undesirable bituminous mixes. Have you written to Prime Minister Modi on this?
Yes, I have. I do not think PM Modi’s “own eyes” have seen my letter. The PM Office informed me that my letter has been sent to MORTH for “information and necessary action”. Obviously, it went to the “status quo” engineers in MORTH and IRC for “necessary action”. You can guess the fate of that letter, it was rejected!
Do you have any hope under such circumstances?
Yes. I am an optimist. I am hoping young, progressive engineers like you who truly believe in the fundamentals of highway engineering would arise one day and will bring about the radical change we have discussed. We have this malignant cancer in our road system, which requires “radical surgery” rather than a band aid.
Prof. Prithvi Singh Kandhal
“American roads are good not because America is rich, but America is rich because American roads are good.” - John F. Kennedy
About the Writer
Prof. Prithvi Singh Kandhal is Associate Director Emeritus of the National Center for Asphalt Technology (NCAT) based at Auburn University, Alabama, U.S.A. NCAT is the largest asphalt (bitumen) road technology center in the world.
Prior to joining NCAT in 1988, Prof. Kandhal served as Chief Asphalt Road Engineer of the Pennsylvania Department of Transportation for 17 years. He is the first person born outside North America, who has held the following three national and international very prestigious positions in the asphalt road technology area:
Ø President, Association of Asphalt Paving Technologists (with members from all continents in the world)
Ø Chairman, American Society for Testing and Materials (ASTM) International Committee on Road Paving Standards (responsible for over 200 standards used worldwide)
Ø Chairman, US Transportation Research Board Committee on Asphalt Roads
Prof. Kandhal has published over 120 technical papers and has co-authored the first ever textbook on asphalt road technology, which is used by more than 25 universities in the U.S. He has travelled to various countries in Europe, South America, Middle East, China, Vietnam, Japan, Singapore, and Australia to provide training and consulting services in asphalt (bitumen) technology.
Prof. Kandhal has been a practicing highway engineer in India for over 20 years and in the US for 30 years. Recently he has drafted many standards for the Indian Roads Congress including specifications for dense graded bituminous mixes, stone matrix asphalt and readymade pothole patching mix. He was also instrumental single-handedly in introducing viscosity grading of bitumen in India in lieu of penetration grading in 2005. He has now published in July 2016 the first ever textbook cum reference book, “Bituminous Road Construction in India”.
In August 2011, Prof. Kandhal was inducted on the “Wall of Honour” established at the largest asphalt road research center in the United States. In April 2012, he received the “Lifetime Achievement Award in Asphalt Road Technology” from the International Association of Asphalt Paving Technologists during their annual banquet held in Austin, Texas, USA.